Gyromagnetic Modes in Waveguide Partially Loaded with Ferrite

Analysis is made of all the propagating modes of a vanishingly small rectangular waveguide partially filled with transversely magnetized ferrite. Each of these modes is shown to propagate in only one directum and to tend to be lossy. Use of these properties can be made in the design of a novel non-resonance isolator. All but one of the propagating modes vary in amplitude along the dc magnetic field. Yet they can apparently be excited experimentally at a boundary by an incident mode, with none of the modes having any variation along the dc field. Theoretical considerations indicate that finite conductivity in the waveguide walls may be responsible for this coupling. The unidirectional properties of these modes suggest the possibility of building purely reactive isolators, but these can be shown nonexistent from general energy considerations. Experiments are described that show that nature resolves this “paradox” by absorbing power, even in low-loss ferrite, rather than reflecting it. Some possible explanations of this behavior are set forth.